Liquid jet apparatus performing pulse modulation on a drive signal

ABSTRACT

A liquid jet apparatus according to the present invention includes a drive waveform generator adapted to generate a drive waveform signal, a modulator adapted to execute pulse modulation on the drive waveform signal, a digital power amplifier adapted to power-amplify the modulated signal, on which the pulse modulation is executed by the modulator, with a pair of switching elements push-pull coupled with each other, a low pass filter adapted to smooth the amplified digital signal obtained by the power-amplification of the digital power amplifier, and a modulation period modification circuit adapted to modify a modulation period of the pulse modulation of the modulator based on data of the drive waveform signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/743,169, filed Jan. 16, 2013, which is a divisional of U.S. patentapplication Ser. No. 12/340,895, filed Dec. 22, 2008, which claimspriority to Japanese patent application no. 2007-331892, filed Dec. 25,2007. The foregoing patent applications are incorporated herein byreference.

BACKGROUND

1. Technical Field

The present invention relates to a liquid jet apparatus arranged to formpredetermined characters and images by emitting microscopic droplets ofliquids from a plurality of nozzles to form the microscopic particles(dots) thereof on a medium.

2. Related Art

Incidentally, in liquid jet printing apparatuses using the liquid jetapparatus, a drive signal amplified by a power amplifying circuit isapplied to an actuator such as a piezoelectric element to emit a jet ofa liquid from a nozzle, and if the drive signal is amplified by ananalog power amplifier such as a linearly driven push-pull coupledtransistor, a substantial power loss is caused, and a large heat sinkfor radiation is required. Therefore, according to JP-A-2005-329710, thedrive signal is amplified using a digital power amplifier, therebyreducing the power loss, and eliminating the heat sink.

In the case of power-amplifying the drive signal using the digital poweramplifier, it is a common practice to execute pulse modulation on adrive waveform signal acting as the basis for the drive signal, and toexecute digital power amplification on the modulated signal.Incidentally, in the case of performing high-quality and high-speedprinting with a one-pass operation using a line head printing apparatus,the time required for printing one dot is extremely short. For example,if a piezoelectric element is used as the actuator, it is required topull in the liquid in the nozzle and then push it out to eject a jetwithin the short time required for printing a dot, and this requires adrive voltage signal with an accurate trapezoidal waveform. Since thedrive waveform signal is as precise as the drive signal, in order forexecuting accurate pulse modulation on the precise drive waveformsignal, it is required to shorten the modulation period, such as theperiod of a triangular wave for pulse-width modulation, or the samplingperiod for pulse-density modulation.

However, if the modulation period is too short, an extremely shorton-duty pulse or off-duty pulse is generated at the low voltage or thehigh voltage in the case of, for example, the pulse-width modulation, oran extremely short on-duty or off-duty pulse is generated at anintermediate voltage in the case of, for example, the pulse-densitymodulation, which causes a problem that the accurate drive signal is notobtained in the case in which the switching element of the digital poweramplifier does not respond to the short pulse. It is obvious that if themodulation period is made longer in order for eliminating this problem,the follow-up property to the drive waveform signal is degraded, andtherefore, the accurate drive signal is not obtained after all.

SUMMARY

The invention has an object of providing a liquid jet apparatus capableof outputting an accurate drive signal while assuring the follow-upproperty of the drive signal to a drive waveform signal when performingpower-amplification using a digital power amplifier.

A liquid jet apparatus according to the invention has a feature ofincluding a drive waveform generator adapted to generate a drivewaveform signal, a modulator adapted to execute pulse modulation on thedrive waveform signal, a digital power amplifier adapted topower-amplify the modulated signal, on which the pulse modulation isexecuted by the modulator, with a pair of switching elements push-pullcoupled with each other, a low pass filter adapted to smooth theamplified digital signal obtained by the power-amplification of thedigital power amplifier, and a modulation period modification circuitadapted to modify a modulation period of the pulse modulation of themodulator based on data of the drive waveform signal.

The modulation period in the invention denotes a basic unit period ofthe pulse modulation such as the triangular wave frequency of thepulse-width modulation (PWM) or the sampling frequency of thepulse-density modulation (PDM). It should be noted that the modulationperiod can be applied to the basic unit period of the pulse modulationin pulse-frequency modulation (PFM) or pulse-phase modulation (PPM).

According to the liquid jet apparatus of the invention, by modifying themodulation period based on the data of the drive waveform signal, it ispossible to prevent such short pulses that the switching elements of thedigital power amplifier cannot respond to, and at the same time, toassure the follow-up property to the drive waveform signal, therebyoutputting the accurate drive signal.

Further, the liquid jet apparatus according to the present invention hasa feature that in the case in which the pulse modulation by themodulator is pulse-width modulation, the modulation period modificationcircuit modifies the modulation period by modifying a frequency of atriangular wave signal of the modulator in accordance with a potentialof the drive waveform signal.

Further, the liquid jet apparatus according to the present invention hasa feature that the modulation period modification circuit modifies thefrequency of the triangular wave signal of the modulator in accordancewith a variation in the potential of the drive waveform signal.

Further, the liquid jet apparatus according to the present invention hasa feature that in the case in which the pulse modulation by themodulator is pulse-density modulation, the modulation periodmodification circuit modifies the modulation period by modifying asampling frequency of the modulator in accordance with a potential ofthe drive waveform signal.

Further, the liquid jet apparatus according to the present invention hasa feature that the modulation period modification circuit modifies thesampling frequency of the modulator in accordance with a variation inthe potential of the drive waveform signal.

Further, a liquid jet apparatus according to the invention has a featureof including a drive waveform generator adapted to generate a drivewaveform signal, a modulator adapted to execute pulse modulation on thedrive waveform signal, a digital power amplifier adapted topower-amplify the modulated signal, on which the pulse modulation isexecuted by the modulator, with a pair of switching elements push-pullcoupled with each other, and a low pass filter adapted to smooth theamplified digital signal obtained by the power-amplification of thedigital power amplifier, wherein the drive waveform generator modifies amodulation period of the pulse modulation of the modulator inconjunction with data of the drive waveform signal.

Further, a liquid jet apparatus according to the invention has a featureof including a drive waveform generator adapted to generate a drivewaveform signal, a modulator adapted to execute pulse modulation on thedrive waveform signal, a digital power amplifier adapted topower-amplify the modulated signal, on which the pulse modulation isexecuted by the modulator, with a pair of switching elements push-pullcoupled with each other, and a low pass filter adapted to smooth theamplified digital signal obtained by the power-amplification of thedigital power amplifier, wherein the drive waveform generator storesmodulation period data of the pulse modulation in conjunction with dataof the drive waveform signal.

Further, the liquid jet apparatus according to the invention has afeature that the drive waveform generator refers to the modulationperiod data in accordance with the drive waveform signal data.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a plan view of a schematic configuration of a liquid jetprinting apparatus using a liquid jet apparatus according to theinvention.

FIG. 1B is a front view of the schematic configuration of the liquid jetprinting apparatus using the liquid jet apparatus according to theinvention.

FIG. 2 is a block diagram of a control device of the liquid jet printingapparatus.

FIG. 3 is an explanatory diagram of a drive signal for driving anactuator.

FIG. 4 is a block diagram of a selection section for coupling the drivesignal with the actuator.

FIG. 5 is a block diagram showing a first embodiment of a drive signaloutput circuit built up in the head driver shown in FIG. 2.

FIG. 6 is a flowchart of arithmetic processing executed in a modulationperiod modification circuit shown in FIG. 5.

FIG. 7 is an explanatory diagram of a modulated signal by the arithmeticprocessing shown in FIG. 6.

FIG. 8 is an explanatory diagram of the modulated signal in a drivesignal output circuit of the related art.

FIG. 9 is an explanatory diagram for setting the frequency of atriangular wave signal.

FIG. 10 is a block diagram showing a second embodiment of the drivesignal output circuit built up in the head driver shown in FIG. 2.

FIG. 11 is a flowchart of arithmetic processing executed in a modulationperiod modification circuit shown in FIG. 10.

FIG. 12 is an explanatory diagram of a modulated signal by thearithmetic processing shown in FIG. 11.

FIG. 13 is an explanatory diagram of the modulated signal in a drivesignal output circuit of the related art.

FIG. 14 is a block diagram showing a third embodiment of the drivesignal output circuit built up in the head driver shown in FIG. 2.

FIG. 15 is a block diagram showing a fourth embodiment of the drivesignal output circuit built up in the head driver shown in FIG. 2.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

A first embodiment of a liquid jet printing apparatus using a liquid jetapparatus of the invention will hereinafter be explained.

FIGS. 1A and 1B are schematic configuration diagrams of the liquid jetprinting apparatus according to the first embodiment, wherein FIG. 1A isa plan view thereof, and FIG. 1B is a front view thereof. In FIGS. 1Aand 1B, in a line head printing apparatus, a print medium 1 is conveyedfrom right to left of the drawing along the arrow direction, and isprinted in a print area in the middle of the conveying path.

The reference numeral 2 denotes first liquid jet heads disposed on theupstream side of the print medium 1 in the conveying direction, thereference numeral 3 denotes second liquid jet heads disposed similarlyon the downstream side, a first conveying section 4 for conveying theprint medium 1 is disposed below the first liquid jet heads 2, and asecond conveying section 5 is disposed below the second liquid jet heads3. The first conveying section 4 is composed of four first conveyingbelts 6 disposed with predetermined intervals in the direction(hereinafter also referred to as a nozzle array direction) traversingthe conveying direction of the print medium 1, and the second conveyingsection 5 is similarly composed of four second conveying belts 7disposed with predetermined intervals in the direction (the nozzle arraydirection) traversing the conveying direction of the print medium 1.

The four first conveying belts 6 and the similar four second conveyingbelts 7 are disposed alternately adjacent to each other. In the firstembodiment, among the conveying belts 6, 7, the two first conveyingbelts 6 and the two second conveying belts 7 on the right side in thenozzle array direction are separated form the two first conveying belts6 and the two second conveying belts 7 on the left side in the nozzlearray direction. In other words, an overlapping portion of the two firstconveying belts 6 and the two second conveying belts 7 on the right sidein the nozzle array direction is provided with a right side drive roller8R, an overlapping portion of the two first conveying belts 6 and thetwo second conveying belts 7 on the left side in the nozzle arraydirection is provided with a left side drive roller 8L, right side firstdriven roller 9R and left side first driven roller 9L are disposed onthe upstream side thereof, and right side second driven roller 10R andleft side second driven roller 10L are disposed on the downstream sidethereof. Although these rollers may seem a series of rollers, actuallythey are decoupled at the center portion of FIG. 1A.

Further, the two first conveying belts 6 on the right side in the nozzlearray direction are wound around the right side drive roller 8R and theright side first driven roller 9R, the two first conveying belts 6 onthe left side in the nozzle array direction are wound around the leftside drive roller 8L and the left side first driven roller 9L, the twosecond conveying belts 7 on the right side in the nozzle array directionare wound around the right side drive roller 8R and the right sidesecond driven roller 10R, the two second conveying belts 7 on the leftside in the nozzle array direction are wound around the left side driveroller 8L and the left side second driven roller 10L, and further, aright side electric motor 11R is coupled to the right side drive roller8R, and a left side electric motor 11L is coupled to the left side driveroller 8L.

Therefore, when the right side electric motor 11R rotationally drivesthe right side drive roller 8R, the first conveying section 4 composedof the two first conveying belts 6 on the right side in the nozzle arraydirection and similarly the second conveying section 5 composed of thetwo second conveying belts 7 on the right side in the nozzle arraydirection move in sync with each other and at the same speed, while theleft side electric motor 11L rotationally drives the left side driveroller 8L, the first conveying section 4 composed of the two firstconveying belts 6 on the left side in the nozzle array direction andsimilarly the second conveying section 5 composed of the two secondconveying belts 7 on the left side in the nozzle array direction move insync with each other and at the same speed. It should be noted that byarranging the rotational speeds of the right side electric motor 11R andthe left side electric motor 11L to be different from each other, theconveying speeds on the left and right in the nozzle array direction canbe set to be different from each other, and specifically, by arrangingthe rotational speed of the right side electric motor 11R to be higherthan the rotational speed of the left side electric motor 11L, theconveying speed on the right side in the nozzle array direction can bemade higher than that on the left side, and by arranging the rotationalspeed of the left side electric motor 11L to be higher than therotational speed of the right side electric motor 11R, the conveyingspeed on the left side in the nozzle array direction can be made higherthan that on the right side. Further, by thus controlling the conveyingspeeds on the respective sides in the nozzle array direction, namely thedirection traversing the conveying direction, it becomes possible tocontrol the conveying posture of the print medium 1.

The first liquid jet heads 2 and the second liquid jet heads 3 aredisposed so as to be shifted from each other in the conveying directionof the print medium 1 corresponding respectively to the four colors,such as yellow (Y), magenta (M), cyan (C), and black (K). The liquid jetheads 2, 3 are supplied with liquids such as ink from liquid tanks ofrespective colors not shown via liquid supply tubes. The liquid jetheads 2, 3 are each provided with a plurality of nozzles formed in thedirection traversing the conveying direction of the print medium 1, andby emitting a necessary amount of the liquid jet from the respectivenozzles simultaneously to the necessary positions, microscopic dots areformed on the print medium 1. By executing the process described abovefor each of the colors, one-pass print can be achieved only by makingthe print medium 1 conveyed by the first and second conveying sections4, 5 pass therethrough once.

As a method of emitting a liquid jet from each of the nozzles of theliquid jet head, there are cited electrostatic driving method,piezoelectric driving method, film boiling liquid jet method, and so on,and in the first embodiment there is used the piezoelectric drivingmethod. In the piezoelectric driving method, when a drive signal isprovided to a piezoelectric element as an actuator, a diaphragm in acavity is displaced to cause pressure variation in the cavity, and theliquid jet is emitted from the nozzle in response to the pressurevariation. Further, by controlling the wave height and the voltagevariation gradient of the drive signal, it becomes possible to controlthe amount of liquid jet to be emitted therefrom. It should be notedthat the actuator formed of a piezoelectric element is a capacitive loadhaving a capacitance.

The nozzles of the first liquid jet head 2 are only provided between thefour first conveying belts 6 of the first conveying section 4, and thenozzles of the second liquid jet head 3 are only provided between thefour second conveying belts 7 of the second conveying section 5.Although this is for cleaning each of the liquid jet heads 2, 3 with acleaning section described later, in this case, the entire surface isnot printed by the one-pass printing if either one of the liquid jetheads is used. Therefore, the first liquid jet heads 2 and the secondliquid jet heads 3 are disposed so as to be shifted in the conveyingdirection of the print medium 1 in order for compensating for eachother's unprintable areas.

Below the first liquid jet heads 2, there are disposed first cleaningcaps 12 for cleaning the first liquid jet heads 2, and below the secondliquid jet heads 3 there are disposed second cleaning caps 13 forcleaning the second liquid jet heads 3. Each of the cleaning caps 12, 13is formed to have a size allowing the cleaning caps to pass through thegaps between the four first conveying belts 6 of the first conveyingsection 4 and the gaps between the four second conveying belts 7 of thesecond conveying section 5. Each of the cleaning caps 12, 13 is composedof a cap body having a rectangular shape with a bottom, covering thenozzles provided to the lower surface, namely a nozzle surface of theliquid jet head 2, 3, and capable of adhering to the nozzle surface, aliquid absorber disposed at the bottom thereof, a peristaltic pumpconnected to the bottom of the cap body, and an elevating device formoving the cap body up and down. Then, the cap body is moved up by theelevating device to be adhered to the nozzle surface of the liquid jethead 2, 3. By applying the negative pressure in the cap body using theperistaltic pump in the present state, the liquid and bubbles aresuctioned from the nozzles opened on the nozzle surface of the liquidjet head 2, 3, thus the cleaning of the liquid jet head 2, 3 can beperformed. After the cleaning is completed, each of the cleaning caps12, 13 is moved down.

On the upstream side of the first driven rollers 9R, 9L, there isprovided a pair of gate rollers 14 for adjusting the feed timing of theprint medium 1 fed from a feeder section 15 and at the same timecorrecting the skew of the print medium 1. The skew denotes a turn ofthe print medium 1 with respect to the conveying direction. Further,above the feeder section 15, there is provided a pickup roller 16 forfeeding the print medium 1. It should be noted that the referencenumeral 17 denotes a gate roller motor for driving the gate rollers 14.

A belt charging device 19 is disposed below the drive rollers 8R, 8L.The belt charging device 19 is composed of charging rollers 20 eachhaving contact with the first conveying belts 6 and the second conveyingbelts 7 by pinching the first conveying belts 6 and the second conveyingbelts 7 between the charging rollers and the drive rollers 8R, 8L, aspring 21 for pressing the charging rollers 20 against the firstconveying belts 6 and the second conveying belts 7, and a power supply18 for providing charge to the charging rollers 20, and charges thefirst conveying belts 6 and the second conveying belts 7 by providingthe first conveying belts 6 and the second conveying belts 7 with thecharge. Since the belts are generally made of a moderate or highresistivity material or an insulating material, when they are charged bythe belt charging device 19, the charge applied on the surface thereofcauses the dielectric polarization on the print medium 1 made similarlyof a high resistivity material or an insulating material, and the printmedium 1 can be absorbed to the belt by the electrostatic force causedbetween the charge generated by the dielectric polarization and thecharge on the surface of the belt. It should be noted that as the beltcharging means, a corotron method for showering the charges can also beused.

Therefore, according to the liquid jet printing apparatus using theliquid jet apparatus of the first embodiment, when the surfaces of thefirst conveying belts 6 and the second conveying belts 7 are charged bythe belt charging device 19, the print medium 1 is fed from the gateroller 14 in that state, and the print medium 1 is pressed against thefirst conveying belts 6 by a sheet pressing roller not shown, the printmedium 1 is absorbed by the surfaces of the first conveying belts 6under the action of dielectric polarization described above. In thisstate, when the electric motors 11R, 11L rotationally drive the driverollers 8R, 8L, the rotational drive force is transmitted to the firstdriven rollers 9R, 9L via the first conveying belts 6.

Thus, while the first conveying belts 6 are moved to the downstream sidein the conveying direction with the print medium 1 absorbed thereto tomove the print medium 1 below the first liquid jet heads 2, printing isperformed by emitting liquid jets from the nozzles provided to the firstliquid jet heads 2. When the printing by the first liquid jet heads 2 iscompleted, the print medium 1 is moved towards downstream side in theconveying direction to be transferred to the second conveying belts 7 ofthe second conveying section 5. As described above, since the secondconveying belts 7 are also provided with the charge on the surfacesthereof by the belt charging device 19, the print medium 1 is absorbedby the surfaces of the second conveying belts 7 under the action of thedielectric polarization described above.

In this state, while the second conveying belts 7 is moved towards thedownstream side in the conveying direction to move the print medium 1below the second liquid jet heads 3, printing is performed by emittingliquid jets from the nozzles provided to the second liquid jet heads 3.After the printing by the second liquid jet heads 3 is completed, theprint medium 1 is moved further to the downstream side in the conveyingdirection, the print medium 1 is ejected to a catch tray whileseparating it from the surfaces of the second conveying belts 7 by aseparating device not shown in the drawings.

Further, when the cleaning of the first and second liquid ejection heads2, 3 is necessary, the first and second cleaning caps 12, 13 are raisedto be adhered to the nozzle surfaces of the first and second liquid jetheads 2, 3 as described above, the cleaning is performed by applyingnegative pressure to the inside of the caps at that state to suction theliquid and bubbles from the nozzles of the first and second liquid jetheads 2, 3, and after then, the first and second cleaning caps 12, 13are moved down.

In the liquid jet printing apparatus using the liquid jet apparatus ofthe first embodiment, there is provided a control device for controllingthe liquid jet printing apparatus. As shown in FIG. 2, the controldevice is configured including an input interface 61 for receiving printdata input from the host computer 60, a control section 62 formed of amicrocomputer for performing the print process based on the print datainput from the input interface 61, a gate roller motor driver 63 forcontrolling and driving the gate roller motor 17, a pickup roller motordriver 64 for controlling and driving a pickup roller motor 51 fordriving the pickup roller 16, a head driver 65 for controlling anddriving the liquid jet heads 2, 3, a right side electric motor driver66R for controlling and driving the right side electric motor 11R, aleft side electric motor driver 66L for controlling and driving the leftside electric motor 11L, and an interface 67 for connecting the gateroller motor driver 63, the pickup roller motor driver 64, the headdriver 65, the right side electric motor driver 66R, and the left sideelectric motor driver 66L respectively to the gate roller motor 17, thepickup roller motor 51, the liquid jet heads 2, 3, the right sideelectric motor 11R, and the left side electric motor 11L.

The control section 62 is provided with a central processing unit (CPU)62 a for performing various processes such as a printing process, arandom access memory (RAM) 62 c for temporarily stores the print datainput via the input interface 61 and various kinds of data used inperforming the printing process of the print data, and for temporarilydeveloping a program, for example, for the printing process, and aread-only memory (ROM) 62 d formed of a nonvolatile semiconductor memoryand for storing, for example, the control program executed by the CPU 62a. When the control section 62 receives the print data (the image data)from the host computer 60 via the input interface 61, the CPU 62 aexecutes a predetermined process on the print data to calculate nozzleselection data and drive signal output data to the nozzle actuatorsregarding which nozzle emits the liquid jet or how much liquid jet isemitted, and outputs the drive signals and the control signals to thegate roller motor driver 63, the pickup roller motor driver 64, the headdriver 65, the right side electric motor driver 66R, and the left sideelectric motor driver 66L, respectively, based on the print data, drivesignal output data, and the input data from the various sensors. Inresponse to the drive signals and the control signals, the actuators 22corresponding to the plurality of nozzles of the liquid jet heads 2, 3,the gate roller motor 17, the pickup roller motor 51, the right sideelectric motor 11R, and the left side electric motor 11L respectivelyoperate to execute the feeding and conveying of the print medium 1, theposture control of the print medium 1, and the printing process on theprint medium 1. It should be noted that the constituents inside thecontrol section 62 are electrically connected to each other via a busnot shown in the drawings.

FIG. 3 shows an example of a drive signal COM supplied from the controldevice of the liquid jet printing apparatus using the liquid jetapparatus according to the first embodiment to the liquid jet heads 2, 3and for driving the actuators 22 each formed of a piezoelectric element.In the first embodiment, the signal is assumed to be a signal with theelectric potential varying around a midpoint potential. The drive signalCOM is formed by connecting drive pulses PCOM as unit drive signals fordriving the actuator 22 so as to emit a liquid jet in a time-seriesmanner, wherein the rising section of each of the drive pulses PCOMcorresponds to a stage of expanding the volume of the cavity (thepressure chamber) communicating with the nozzle to pull in the liquid(it can also be said that the meniscus is pulled in, in view of thesurface of the liquid to be emitted), the falling section of each of thedrive pulses PCOM corresponds to a stage of reducing the volume of thecavity to push out the liquid (it can also be said that the meniscus ispushed out, in view of the surface of the liquid to be emitted), and asa result of pushing out the liquid, the liquid jet is emitted from thenozzle.

By variously modifying the gradient of increase and decrease in voltageand the height of the drive pulse PCOM formed of this trapezoidalvoltage wave, the pull-in amount and the pull-in speed of the liquid,and the push-out amount and the push-out speed of the liquid can bemodified, thus the amount of liquid jet can be varied to obtain theliquid dots with different sizes. Therefore, in the case in which aplurality of drive pulses PCOM are sequentially joined, it is possibleto select the single drive pulse PCOM from the drive pulses to besupplied to the actuator to emit the liquid jet, or to select the two ormore drive pulses PCOM to be supplied to the actuator to emit the liquidjet two or more times, thereby obtaining the dots with various sizes. Inother words, when the two or more liquid droplets land on the sameposition before the liquid is dried, it brings substantially the sameresult as emitting a larger amount of liquid jet, thus the size of thedot can be enlarged. By a combination of such technologies, it becomespossible to achieve multiple tone printing. It should be noted that thedrive pulse PCOM1 shown in the left end of FIG. 3 is only for pulling inthe liquid without pushing out the liquid. This is called a finevibration, and is used for preventing thickening in the nozzle withoutemitting the liquid jet.

As a result of the above, in the liquid jet head 2, 3 there are inputthe drive signal COM output from the drive signal output circuitdescribed later, the drive pulse selection data SI & SP for selectingthe nozzle to emit the liquid jet and determining the coupling timing ofthe actuator 22 such as a piezoelectric element to the drive signal COMbased on the print data, the latch signal LAT and a channel signal CHfor coupling the drive signals COM with the actuators 22 of the liquidjet head 2, 3 to each other based on the drive pulse selection data SI &SP after the nozzle selection data is input to all of the nozzles, andthe clock signal SCK for transmitting the drive pulse selection data SI& SP to the liquid jet head 2, 3 as a serial signal. It should be notedthat it is hereinafter assumed that the minimum unit of the drive signalfor driving the actuator 22 is the drive pulse PCOM, and the entiresignal having the drive pulses PCOM coupled with each other in a timeseries manner is described as the drive signal COM.

Then, the configuration of coupling the drive signals COM output fromthe drive circuit with the actuators 22 such as a piezoelectric elementwill be explained. FIG. 4 is a block diagram of the selection sectionfor coupling the drive signals COM with the actuators such as thepiezoelectric element. The selection section is composed of a shiftregister 211 for storing the drive pulse selection data SI & SP fordesignating the actuator 22 such as a piezoelectric elementcorresponding to the nozzle from which the liquid jet is to be emitted,a latch circuit 212 for temporarily storing the data of the shiftregister 211, a level shifter 213 for executing level conversion on theoutput of the latch circuit 212, and a selection switch 201 for couplingthe drive signal COM with the actuator 22 such as a piezoelectricelement in accordance with the output of the level shifter.

The drive pulse selection data SI & SP is sequentially input to theshift register 211, and at the same time, the storage area issequentially shifted from the first stage to the subsequent stage inaccordance with the input pulse of the clock signal SCK. The latchcircuit 212 latches the output signals of the shift register 211 inaccordance with the latch signal LAT input thereto after the drive pulseselection data SI & SP corresponding to the number of the nozzles isstored in the shift register 211. The signals stored in the latchcircuit 212 are converted to have the voltage levels capable ofswitching on and off the selection switch 201 on the subsequent stage bythe level shifter 213. This is because the drive signal COM has a highvoltage compared to the output voltage of the latch circuit 212, and theoperating voltage range of the selection switch 210 is also set to behigher accordingly. Therefore, the actuator 22 such as piezoelectricelement the selection switch 201 of which is closed by the level shifter213 is coupled with the drive signal COM (the drive pulse PCOM) at thecoupling timing of the drive pulse selection data SI & SP. Further,after the drive pulse selection data SI & SP of the shift register 211is stored in the latch circuit 212, the subsequent print information isinput to the shift register 211, and the stored data of the latchcircuit 212 is sequentially updated at the liquid jet emission timing.It should be noted that the reference symbol HGND denotes the groundterminal for the actuator 22 such as the piezoelectric element. Further,according to the selection switch 201, even after the actuator 22 suchas the piezoelectric element is separated from the drive signal COM (thedrive pulse PCOM), the input voltage of the actuator 22 is maintained atthe voltage immediately before it is separated.

FIG. 5 shows an example of a specific configuration of the drive signaloutput circuit in the head driver 65 for driving the actuator 22. Thedrive signal output circuit is configured including a drive waveformgenerator 25 for generating a drive waveform signal WCOM forming a baseof the drive signal COM (the drive pulse PCOM), namely a basis of asignal for controlling driving of the actuators 22 based on the drivesignal output data from the control section 62, a modulator 26 forexecuting pulse modulation on the drive waveform signal WCOM generatedby the drive waveform generator 25, a digital power amplifier 28 forpower-amplifying the modulated signal on which the pulse modulation isexecuted by the modulator 26, and a low pass filter 29 for smoothing theamplified digital signal power-amplified by the digital power amplifier28 and supplying the actuators 22 with the amplified digital signal thussmoothed as the drive signal COM (the drive pulse PCOM).

The drive waveform generator 25 combines predetermined digital electricpotential data in a time-series manner and output the combinedpredetermined digital electric potential data, and further executesanalog conversion thereon with a D/A converter to output it as the drivewaveform signal WCOM. In the first embodiment, as the modulator 26 forperforming the pulse modulation on the drive waveform signal WCOM, thereis used a typical pulse width modulation (PWM) circuit. In the pulsewidth modulation, the triangular wave generator 23 generates atriangular wave signal with a predetermined frequency, and a comparator24 compares the triangular wave signal with the drive waveform signalWCOM to output a pulse signal taking on-duty when, for example, thedrive waveform signal WCOM is greater than the triangular wave signal,as the modulated signal. The digital power amplifier 28 is configuredincluding a half-bridge output stage 31 formed of a high-side switchingelement Q₁ and a low-side switching element Q₂ for substantiallyamplifying the power, and a gate driver circuit 30 for controllinggate-source signals GH, GL of the switching elements Q₁, Q₂ based on themodulated signal from the modulator 26. Further, the low pass filter 29is formed of a low pass filter composed of a combination of inductorsand capacitances, and the low pass filter eliminates the modulationperiod component of the amplified digital signal, namely the frequencycomponent of the triangular wave signal in this case.

In the digital power amplifier 28, when the modulated signal is in an Hilevel, the gate-source signal GH of the high-side switching element Q₁becomes in the Hi level and the gate-source signal GL of the low-sideswitching element Q₂ becomes in an Lo level, and consequently, thehigh-side switching element Q₁ becomes in the ON state and the low-sideswitching element Q₂ becomes in the OFF state, and as a result, theoutput of the half-bridge output stage 31 becomes to have the powersupply voltage VDD. On the other hand, when the modulated signal is inthe Lo level, the gate-source signal GH of the high-side switchingelement Q₁ becomes in the Lo level and the gate-source signal GL of thelow-side switching element Q₂ becomes in the Hi level, and consequently,the high-side switching element Q₁ becomes in the OFF state and thelow-side switching element Q₂ becomes in the ON state, and as a result,the output of the half-bridge output stage 31 becomes 0.

Although a current flows through the switching element in the ON statewhen the high-side and low-side switching elements Q₁, Q₂ are drivendigitally as described above, the resistance value between the drain andthe source is extremely small, and therefore, only a little loss iscaused. Further, since no current flows in the switching element in theOFF state, the power loss does not occur. Therefore, since the loss ofthe digital power amplifier 28 is extremely small, a switching elementsuch as a small-sized MOSFET can be used therefor, and cooling meanssuch as a heat radiation plate for cooling can also be eliminated.Incidentally, the efficiency in the case in which the transistor isdriven in the linear range is about 30% while the efficiency of digitalpower amplifier 28 is 90% or higher. Further, since the heat radiationplate for cooling the transistor requires about 60 mm square in size foreach transistor, if such a radiation plate for cooling can beeliminated, an overwhelming advantage in the actual layout can beobtained.

The frequency of the triangular wave signal generated by the triangularwave signal generator 23, namely the modulation period can be modifiedand set by a modulation period modification circuit 27. In themodulation period modification circuit 27, the arithmetic processingshown in FIG. 6 is executed in a predetermined cycle. In the arithmeticprocessing shown in FIG. 6, potential data of the drive waveform signaland gradient data of increase and decrease in the potential are readfirstly in the step S1.

Then, the process proceeds to the step S2, and whether or not there isno variation in the potential data of the drive waveform signal and atthe same time the gradient data is 0 is determined, and if there is novariation in the potential data of the drive waveform signal and at thesame time the gradient data is 0, the process proceeds to the step S3,otherwise the process proceeds to the step S4.

In the step S3, the frequency of the triangular wave signal is set to bea predetermined low frequency f₂, and the process proceeds to the stepS5.

On the other hand, in the step S4, the frequency of the triangular wavesignal is set to be a predetermined high frequency f₁, and the processproceeds to the step S5.

In the step S5, an instruction of generating and then outputting thetriangular wave signal with the frequency set in the step S3 or the stepS4 is output to the triangular wave signal generator 23, and the processreturns to the main program.

FIG. 7 shows temporal variations of the drive waveform signal, thetriangular wave signal, and the modulated signal (PWM) in the firstembodiment. As the drive waveform signal, the drive pulses for the finevibration described above are used. The modulated signal (PWM)corresponds to the gate-source signal GH to the high-side switchingelement Q₁ of the digital power amplifier 28. In the first embodiment,since the frequency of the triangular wave signal is modified inaccordance with the condition of the variation in the potential of thedrive waveform signal, specifically the frequency of the triangular wavesignal is set to be the predetermined high frequency f₁ in the case inwhich the potential of the drive waveform signal varies, and thefrequency of the triangular wave signal is set to be the predeterminedlow frequency f₂ in the case in which the potential of the drivewaveform signal does not vary, even if the potential is the same, thepulse width of the modulated signal (PWM) in the case in which thepotential of the drive waveform signal varies has the narrow on-duty andthe narrow off-duty, and the pulse width of the modulated signal (PWM)in the case in which the potential of the drive waveform signal does notvary has the large on-duty and the large off-duty. If the frequency ofthe triangular wave signal, namely a so-called carrier frequency ishigh, the follow-up property to the drive waveform signal becomes high.On the other hand, if the pulse width is large, the on-duty and theoff-duty do not easily exceed the response limit of the switchingelements Q₁, Q₂ of the digital power amplifier 28.

FIG. 8 shows the modulated signal (PWM) when setting the frequency ofthe triangular wave signal to be constantly the predetermined highfrequency f₁ in order for assuring the follow-up property of the pulsemodulation with respect to the drive waveform signal. In this case,although there arises no problem in the follow-up property of the pulsemodulation when the potential of the drive waveform signal varies, inthe case in which the drive waveform signal is constantly at a lowpotential, the on-duty pulse width is extremely narrow, and in the casein which the drive waveform signal is constantly in a high potential,the off-duty pulse width is extremely narrow. If such pulses with thenarrow width exceed the response limit of the switching elements Q₁, Q₂of the digital power amplifier 28, the switching elements are notaccurately switched on and off, and therefore, the drive signal outputtherefrom does not become what is obtained by accuratelypower-amplifying the drive waveform signal.

For example, a relationship between the frequency of the triangular wavesignal and the on-duty or off-duty pulse width of the modulated signal(PWM) in the case in which the potential of the drive waveform signal isat a certain level is as shown in FIG. 9, and if the pulse width S₀ ofthe modulated signal (PWM) when the frequency of the triangular wavesignal is f₀ exceeds the response limit of the switching elements Q₁, Q₂of the digital power amplifier 28, it is required to set the frequencyf′₀ corresponding to the pulse width S′₀ of the modulated signal (PWM)not exceeding the response limit of the switching elements Q₁, Q₂ of thedigital power amplifier 28 as the frequency of the triangular wavesignal. What is set in the manner as described above is thepredetermined low frequency f₂ described above.

As described above, according to the liquid jet apparatus of the firstembodiment, since there is adopted the configuration in which the drivewaveform generator 25 generates the drive waveform signal to be thebasis for driving the actuators 22 for emitting the liquid jet, themodulator 26 executes the pulse modulation on the drive waveform signal,the pair of push-pull coupled switching elements of the digital poweramplifier 28 power-amplifies the modulated signal, and the modulationperiod modification circuit 27 modifies the modulation period of thepulse modulation based on the data of the drive waveform signal whensmoothing the amplified digital signal with the low pass filter 29 andoutputting it to the actuator 22, it is possible to prevent such shortpulses that the switching elements Q₁, Q₂ of the digital power amplifier28 cannot respond to, and at the same time, to assure the follow-upproperty to the drive waveform signal by making the modulation periodlonger when the potential of the drive waveform signal does not vary,and shorter when the potential of the drive waveform signal varies,thereby outputting the accurate drive signals.

Further, since there is adopted the configuration of modifying thefrequency of the triangular wave signal of the modulator in accordancewith the condition of the variation in the potential of the drivewaveform signal in the case in which the pulse modulation by themodulator is the pulse-width modulation, it is easy to put the inventioninto practice.

Further, since there is adopted the configuration of making thetriangular wave frequency lower when the potential of the drive waveformsignal does not vary, and making the frequency of the triangular wavesignal of the modulator higher when the potential of the drive waveformsignal varies, it is possible to prevent such short pulses that theswitching elements Q₁, Q₂ of the digital power amplifier 28 cannotrespond to, and at the same time, to assure the follow-up property tothe drive waveform signal.

Then, as a second embodiment applying the liquid jet apparatus of theinvention to the liquid jet printing apparatus, another example of thespecific configuration of the drive signal output circuit in the headdriver 65 for driving the actuators 22 is shown in FIG. 10. FIG. 10includes a number of constituents identical to those of theconfiguration shown in FIG. 5, and since those constituents essentiallyhave substantially the same functions, the equivalent constituents aredenoted with the equivalent numeral references, and the detailedexplanations therefor will be omitted. It is assumed that the drivesignal output circuit, namely the drive waveform generator 25, thedigital power amplifier 28, and the low pass filter 29 of the secondembodiment, have equivalent functions to those shown in FIG. 5 of thefirst embodiment.

In the second embodiment, a pulse-density modulation (PDM) circuit isused as the modulator 26. The pulse density modulator is for performinga well-known ΔΣ modulation at a predetermined sampling period, therebyperforming modulation in a manner that the higher the potential is, thelarger the width of the modulated pulse becomes. Therefore, themodulation period modification circuit 27 modifies the sampling periodof the pulse density modulation executed in the modulator 26. In themodulation period modification circuit 27, the arithmetic processingshown in FIG. 11 is executed in a predetermined cycle. In the arithmeticprocessing shown in FIG. 11, the potential data of the drive waveformsignal and the gradient data of increase and decrease in the potentialare read firstly in the step S1′.

Then, the process proceeds to the step S2′, and whether or not there isno variation in the potential data of the drive waveform signal and atthe same time the gradient data is 0 is determined, and if there is novariation in the potential data of the drive waveform signal and at thesame time the gradient data is 0, the process proceeds to the step S3′,otherwise the process proceeds to the step S4′.

In the step S3′, the sampling frequency of the pulse density modulationis set to be the predetermined low frequency f₂, and then the processreturns to the main program.

On the other hand, in the step S4′, the sampling frequency of the pulsedensity modulation is set to be the predetermined high frequency f₁, andthen the process returns to the main program.

FIG. 12 shows temporal variations of the sampling frequency of thepulse-density modulation, the drive waveform signal, and the modulatedsignal (PDM) in the second embodiment. As the drive waveform signal, thenormal drive pulses described above are used. The start potential of thenormal drive pulse is an intermediate potential. The modulated signal(PDM) corresponds to the gate-source signal GH to the high-sideswitching element Q₁ of the digital power amplifier 28. In the secondembodiment, since the sampling frequency of the pulse-density modulationis modified in accordance with the condition of the variation in thepotential of the drive waveform signal, specifically the samplingfrequency is set to be the predetermined high frequency f₁ in the casein which the potential of the drive waveform signal varies, and thesampling frequency is set to be the predetermined low frequency f₂ inthe case in which the potential of the drive waveform signal does notvary, providing the potential is the same, either one of the on-duty andthe off-duty of the pulse width of the modulated signal (PDM) in thecase in which the potential of the drive waveform signal varies isnarrow, and either one of the on-duty and the off-duty of the pulsewidth of the modulated signal (PDM) in the case in which the potentialof the drive waveform signal does not vary is large. The higher thesampling frequency is, the higher the follow-up property to the drivewaveform signal becomes.

FIG. 13 shows the modulated signal (PDM) when setting the samplingfrequency to be constantly the predetermined high frequency f₁ in orderfor assuring the follow-up property of the pulse modulation with respectto the drive waveform signal. In this case, although there arises noproblem in the follow-up property of the pulse modulation when thepotential of the drive waveform signal varies, the pulse width isextremely narrow in both of the on-duty and the off-duty when the drivewaveform signal is constantly in an intermediate potential. In otherwords, the pitch of the pulses is extremely short. If such pulses withthe narrow width and the short pitch exceed the response limit of theswitching elements Q₁, Q₂ of the digital power amplifier 28, theswitching elements are not accurately switched on and off, andtherefore, the drive signal output therefrom does not become what isobtained by accurately power-amplifying the drive waveform signal.Therefore, in such a case, it is required to set the sampling frequencyin the intermediate potential to be the predetermined low frequency f₂in the same manner as shown in FIG. 8 of the first embodiment.

As described above, according to the liquid jet apparatus of the secondembodiment, since there is adopted the configuration of modifying thesampling frequency of the modulator 26 in accordance with the conditionof the variation in the potential of the drive waveform signal WCOM inthe case in which the pulse modulation by the modulator 26 is thepulse-density modulation, thereby modifying the modulation period, it iseasy to put the invention into practice.

Further, since there is adopted the configuration of modifying thesampling frequency of the modulator in accordance with the potential ofthe drive waveform signal, it is possible to prevent such short pulsesthat the switching elements Q₁, Q₂ of the digital power amplifier 28cannot respond to, and at the same time, to assure the follow-upproperty to the drive waveform signal.

Then, as a third embodiment applying the liquid jet apparatus of theinvention to the liquid jet printing apparatus, another example of thespecific configuration of the drive signal output circuit in the headdriver 65 for driving the actuators 22 is shown in FIG. 14. FIG. 14includes a number of constituents identical to those of theconfiguration shown in FIG. 5, and since those constituents essentiallyhave substantially the same functions, the equivalent constituents aredenoted with the equivalent numeral references, and the detailedexplanations therefor will be omitted. It is assumed that the drivesignal output circuit, namely the modulator 26, the digital poweramplifier 28, and the low-pass filter 29 of the third embodiment, haveequivalent functions to those shown in FIG. 5 of the first embodiment.

In the third embodiment, there is adopted a configuration in which thedrive waveform generator 25 stores frequency data of the triangular wavesignal of the triangular wave generator 23 in the modulator 26 inconjunction with the digital electric potential data of the drivewaveform signal WCOM, and outputs the frequency data to the triangularwave generator 23 in sync with the digital electric potential data ofthe drive waveform signal WCOM. Similarly to the first embodiment, thefrequency data of the triangular wave signal is arranged so that themodulation period is set with modification by raising the frequency ofthe triangular wave signal when the potential of the drive waveformsignal WCOM varies. The operation by the third embodiment is equivalentto that of the first embodiment described above.

Then, as a fourth embodiment applying the liquid jet apparatus of theinvention to the liquid jet printing apparatus, another example of thespecific configuration of the drive signal output circuit in the headdriver 65 for driving the actuators 22 is shown in FIG. 15. The drawingincludes a number of constituents identical to those of theconfiguration shown in FIG. 10, and since those constituents essentiallyhave substantially the same functions, the equivalent constituents aredenoted with the equivalent numeral references, and the detailedexplanations therefor will be omitted. It is assumed that the drivesignal output circuit, namely the modulator 26, the digital poweramplifier 28, and the low-pass filter 29 of the fourth embodiment, haveequivalent functions to those shown in FIG. 10 of the second embodiment.

In the fourth embodiment, there is adopted a configuration in which thedrive waveform generator 25 stores sampling frequency data of thepulse-density modulation executed in the modulator 26 in conjunctionwith the digital electric potential data of the drive waveform signalWCOM, and outputs the frequency data to the modulator 26 in sync withthe digital electric potential data of the drive waveform signal WCOM.Similarly to the second embodiment, the sampling frequency data isarranged so that the modulation period is set with modification byraising the sampling frequency when the potential of the drive waveformsignal WCOM varies. The operation by the fourth embodiment is equivalentto that of the second embodiment described above.

As described above, according to the liquid jet apparatus of the fourthembodiment, since there is adopted the configuration in which the drivewaveform generator 25 generates the drive waveform signal to be thebasis for driving the actuators 22 for emitting the liquid jet, themodulator 26 executes the pulse modulation on the drive waveform signal,the pair of push-pull coupled switching elements of the digital poweramplifier 28 power-amplifies the modulated signal, and the drivewaveform generator 25 modifies the modulation period of the pulsemodulation by the modulator 26 in conjunction with the data of the drivewaveform signal when smoothing the amplified digital signal with the lowpass filter 29 and outputting it to the actuator 22, it is possible toprevent such short pulses that the switching elements Q₁, Q₂ of thedigital power amplifier 28 cannot respond to, and at the same time, toassure the follow-up property to the drive waveform signal by modifyingthe modulation period when the potential of the drive waveform signalvaries, thereby outputting the accurate drive signals.

Further, since the drive waveform generator is arranged to have theconfiguration of storing the modulation period data of the pulsemodulation in conjunction with the data of the drive waveform signal, itbecomes easy to configure the apparatus, and it is easy to put theinvention into practice.

Further, since there is adopted the configuration in which the drivewaveform generator stores the modulation data having the shortermodulation period when the potential of the drive waveform signalvaries, it is possible to prevent such short pulses that the switchingelements Q₁, Q₂ of the digital power amplifier 28 cannot respond to, andat the same time, to assure the follow-up property to the drive waveformsignal.

It should be noted that although in the embodiments describedhereinabove the modulation period is modified to be the two levels, thehigh frequency and the low frequency, the modification of the modulationperiod is not limited thereto, but the modulation period can be arrangedto be variably modified in accordance with, for example, the conditionof the variation in the drive waveform signal.

Further, although in each of the embodiments described above only thecase in which the liquid jet apparatus of the invention is applied tothe line head-type printing apparatus is described in detail, the liquidjet apparatus of the invention can also be applied to multi-passprinting apparatuses in a similar manner.

Further, the liquid jet apparatus of the invention can also be embodiedas a liquid jet apparatus for emitting a jet of a liquid (including aliquid like member dispersing particles of functional materials, and afluid such as a gel besides liquids) other than the ink, or a fluid(e.g., a solid substance capable of flowing as a fluid and being emittedas a jet) other than liquids. The liquid jet device can be, for example,a liquid jet apparatus for emitting a jet of a liquid including amaterial such as an electrode material or a color material used formanufacturing a liquid crystal display, an electroluminescence (EL)display, a plane emission display, or a color filter in a form of adispersion or a solution, a liquid jet apparatus for emitting a jet of aliving organic material used for manufacturing a biochip, or a liquidjet apparatus used as a precision pipette for emitting a jet of a liquidto be a sample. Further, the liquid jet apparatus can be a liquid jetapparatus for emitting a jet of lubricating oil to a precision machinesuch as a timepiece or a camera in a pinpoint manner, a liquid jetapparatus for emitting on a substrate a jet of a liquid of transparentresin such as ultraviolet curing resin for forming a fine hemisphericallens (optical lens) used for an optical communication device, a liquidjet apparatus for emitting a jet of an etching liquid of an acid or analkali for etching a substrate or the like, a fluid jet apparatus foremitting a gel jet, or a fluid jet recording apparatus for emitting ajet of a solid substance including fine particles such as a toner as anexample. Further, the invention can be applied to either one of thesejet apparatuses.

What is claimed is:
 1. A liquid jet apparatus comprising: a drivewaveform generator adapted to generate a drive waveform signal; amodulator adapted to execute pulse modulation on the drive waveformsignal; a digital power amplifier adapted to power-amplify the modulatedsignal, on which the pulse modulation is executed by the modulator; anda low pass filter adapted to smooth the amplified digital signalobtained by the power-amplification of the digital power amplifier,wherein the drive waveform generator stores a sampling frequency data ofthe pulse modulation in conjunction with data of the drive waveformsignal, the sampling frequency data beings arranged so that themodulation period is set with modification by raising the samplingfrequency when the potential of the drive waveform signal varies.